A solid polymer electrolyte fuel cell (Polymer Electrolyte Fuel Cell: hereinafter called “PEFC” as needed) has been developed as a fuel cell vehicle, a home cogeneration system, and the like.
As a catalyst used for the gas diffusion electrode of PEFC, a noble metal catalyst composed of a noble metal of platinum group elements such as platinum (Pt) has been used.
For example, as a typical conventional catalyst, there has been known “Pt on carbon catalyst” which is a powder of catalyst particles where Pt fine particles are supported on an electrically conductive carbon powder (hereinafter called “Pt/C catalyst” as needed).
For example, as the Pt/C catalyst, there has been known a Pt/C catalyst having a Pt support rate of 50 wt %, Trade Name: “NE-F50” available from N. E. CHEMCAT.
In the production costs of PEFC, a proportion of the noble metal catalyst such as Pt is large, and it is the problem to lower the PEFC cost and to spread PEFC.
To solve the problem, developments of technique for lowering the Pt in the catalyst layer of PEFC have been progressed. For example, in Non-Patent Document 1, there is described a summary of the developments until now.
Among these developments, in order to reduce the amount of platinum to fee used, a powder (hereinafter called “core-shell catalyst” as needed) of a catalyst particle having a core-shell structure formed by a core part made of non-platinum element and a shell part made of Pt (hereinafter called “core-shell catalyst particle” as needed) has been studied, and there are many reports.
For example, in Patent Document 1, there is disclosed a particle composite material (corresponding to the core-shell catalyst particle) having a structure where palladium (Pd) or a Pd alloy (corresponding to the core part) is covered with an atomic thin layer of Pt atom (corresponding to shell part). Further in Example of this Patent Document 1, a core-shell catalyst particle having a structure where the core part is a Pd particle and the shell part is a layer made of Pt is described.
Incidentally, the present applicant submits, as publication where the above-mentioned publicly-known inventions are described, the following publication: